Common mode noise filters have large impedance for common mode signals to remove common mode noises. The common mode noise filters have small impedance for differential mode signals, necessary signals, to prevent the signal from being distorted.
FIG. 12 is an exploded perspective view of conventional common mode noise filter 180 disclosed in Japanese Patent Laid-Open Publication No. 2002-203718. Filter 180 includes insulating magnetic substrates 110A and 110B and insulator layers 120A to 120D made of nonmagnetic material. Insulator layers 120A to 120D have spiral coil patterns 130, 140, 150, and 160 formed thereon. Insulator layers 120A to 120D are stacked to form insulating block 120 made of the nonmagnetic material. Coil patterns 130, 140, 150, and 160 are embedded in insulating block 120, and are sandwiched between magnetic substrates 110A and 110B, thus providing common mode noise filter 180. Coil patterns 130, 140, 150, and 160 provide two coils having terminals electrically connected with external edge electrodes, respectively.
Conventional common mode noise filter 180 has a small bonding strength to dielectric block 120 of the external edge electrodes due to decreasing of the area of the external edge electrodes according to reducing of its size. Filter 180 may have low reliability to be mounted on a portable electronic device.